Composite for protection against wind and wind blown debris

ABSTRACT

A composite suitable as an integral portion of a building affording protection from wind blown debris such as from a tornado comprises in order a layer of structural sheathing material such as plywood, a layer of adhesive, a lightweight material, a layer of adhesive, a layer of fabric of high strength fibers bonded resin, a layer of adhesive, and a layer of a structural sheathing material.

TECHNICAL FIELD

The invention relates to the use of a high strength composite sheathingto resist penetration by wind and wind-borne debris such as thatgenerated by severe storm events, particularly tornadoes.

BACKGROUND OF THE INVENTION

Storm shelters and cellars are necessary to provide a safe haven forprotection against severe storm events in regions prone to tornado orhurricane activity. These shelters have been typically constructed ofpoured concrete, steel reinforced masonry, or heavy weight sheet metal.Details of adequate designs for storm shelters and cellars are detailedin publications from the Federal Emergency Management Agency (FEMA) suchas Taking Shelter from the Storm—Publication 320 and Design andConstruction Guidance for Community Shelters—Publication 361. Thecurrent designs rely on the use of common heavyweight constructionmaterials such as concrete and steel to provide the resistance towind-borne debris generated in the storm event.

The current designs are not easily incorporated into current buildingpractices, and result in significant weight increases in the wallstructure. The wood framing approaches described in FEMA Publication 320require the in-filling of the wall section with solid masonry orcontinuous sheathing with 14 gauge steel plate. Doors for these sheltersrequired the reinforcement with a minimum 14-gauge sheet metal toprovide the needed penetration resistance. These approaches arecumbersome, difficult to install and difficult to field work to size. Inregards to doors, the current solutions result in heavyweight doors thatintroduce safety issues and poor aesthetics.

A report dated May 31, 2000 by Clemson University submitted to theFederal Emergency Management Agency entitled “Enhanced Protection forSevere Wind Storms” describes several additional approaches for thereinforcement of shelter walls against wind-borne debris. Conceptsincluded 4 walls (numbers 9, 10, 11 & 17) that made use of Kevlar®cloth. FIG. 12 on page 36 shows that these flexible cloth conceptsprovided no more than 44% of the impact resistance required to meet the“National Performance Criteria for Tornado Shelters”. No conceptproposed in this study provided more than 60% of the requirements.

U.S. 2003-0079430 A1 published May 1, 2003 discloses a fiber reinforcedcomposite sheathing employing a fabric of high strength fibers bondedwith resin in combination with structural sheathing. The composite hasan ability to withstand a 15-pound projectile at a speed of 161kilometers (100 miles) per hour.

U.S. patent application Ser. No. 10/308,492 sets forth the composite ofU.S. 2003-0079430 A1 in combination with a layer of material having adensity not greater than 0.25 grams per cubic centimeter.

A substantial need exists for a method of forming a composite usinglightweight field friendly materials to provide protection from wind andwind-borne debris such as that generated in tornadoes and hurricanes.However, wind speeds generated by tornadoes can exceed 200 miles perhour which is greatly in excess of wind speeds generated by hurricanes.Therefore, a particular need exists for the lightweight field workablesheathing to withstand both wind and wind-borne debris generated by thehigher tornado wind speeds.

SUMMARY OF THE INVENTION

The present invention is directed to:

-   -   a composite comprising in order:    -   (a) a layer of structural sheathing,    -   (b) a layer of adhesive,    -   (c) a layer of material having a density not greater than 0.25        grams per cubic centimeter,    -   (d) a layer of adhesive,    -   (e) a layer of a fabric containing high strength fibers bonded        with a resin,    -   (f) a layer of adhesive,    -   (g) a layer of structural sheathing.        wherein the fabric layer will deflect in a range from 5.0 to        17.5 centimeters when impacted by a 6.8-kilogram (15 pound)        projectile at a speed of 161 kilometers (100 miles) per hour in        accordance with ASTM test procedure E1886-97.

The adhesively bonded composite can be designed to meet both the windpressure and windborne debris requirements by selection of the core andstructural sheathing properties, so as to meet the specifications listedabove, and in accordance with available structural design formula forfoam filled structures. These formulas can be found in publications suchas “Design of Foam-Filled Structures,” by John Hartsock, and “Design andFabrication of Plywood Sandwich Panels” published by the AmericanPlywood Association.

The composite is particularly adapted for construction of storm sheltersand residences located in areas of the world which are subjected towind-blown debris not only by hurricanes but also from the substantiallyhigher wind speeds of tornadoes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 represents a load deflection curve for an 86-inch long panel ofExamples 1, 2 and 3 in accordance with ASTM E72 Traverse Load Test.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improvement in formation of a compositeemploying a high strength bonded fabric layer as defined in the Summaryof the Invention. Although the high strength bonding fabric layer incombination with structural sheathing is highly effective in providingprotection against wind blown debris, a need is present for protectionagainst the force of only wind in a free standing composite.

The present invention overcomes a need for a robust and/or complicatedframing structure to hold a composite in place. Due to rigidity yet asthe same time flexibility in the composite, protection is obtained fromthe effects of wind per se and wind blown debris.

Rigidity in the composite is necessary to obtain protection opposite airpressure generated due to wind speed. Flexibility is present in thecomposite opposite wind blown debris wherein debris can puncture anouter sheathing before striking a high strength bonded fabric which willdeflect in a range of 5.0 to 17.5 centimeters when impacted by a 6.8kilogram (15 pound) projectile at a speed of 161 kilometers (100 miles)per hour in accordance with ASTM test procedure E1886-97.

Therefore, a necessary component for protection against wind-blowndebris such as generated by tornadoes with wind speeds in excess of 200miles per hour is a fabric containing high strength fiber. The fabricmay be a woven or non-woven although a woven fabric is preferred. Highstrength fibers are well known and as employed herein means fibershaving a tenacity of at least 10 grams per dtex and a tensile modulus ofat least 150 grams per dtex. Yarns can be made from fibers such asaramids, polyolefins, polybenzoxazole, polybenzothiazole, glass and thelike, and may be made from mixtures of such yarns.

The fabric may include up to 100 percent aramid fiber. By “aramid” ismeant a polyamide wherein at least 85% of the amide (—CO—NH—) linkagesare attached directly to two aromatic rings. Examples of aramid fibersare described in Man-Made Fibers-Science and Technology₁ Volume 2,Section titled Fiber-Forming Aromatic Polyamides, page 297, W. Black etal., Interscience Publishers, 1968. Aramid fibers are, also, disclosedin U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587; 3,673,143; 3,354,127;and 3,094,511.

Para-aramids are common polymers in aramid yarn and poly(p-phenyleneterephthalamide) (PPD-T) is a common para-aramid. By PPD-T is meant thehomopolymer resulting from mole-for-mole polymerization of p-phenylenediamine and terephthaloyl chloride and, also, copolymers resulting fromincorporation of small amounts of other diamines with the p-phenylenediamine and of small amounts of other diacid chlorides with theterephthaloyl chloride. As a general rule, other diamines and otherdiacid chlorides can be used in amounts up to as much as about 10 molepercent of the p-phenylene diamine or the terephthaloyl chloride, orperhaps slightly higher, provided only that the other diamines anddiacid chlorides have no reactive groups which interfere with thepolymerization reaction. PPD-T, also, means copolymers resulting fromincorporation of other aromatic diamines and other aromatic diacidchlorides such as, for example, 2,6-naphthaloylchloride or chloro- ordichloroterephthaloyl chloride or 3,4 -diaminodiphenylether.

By “polyolefin” is meant polyethylene or polypropylene. By polyethyleneis meant a predominantly linear polyethylene material of preferably morethan one million molecular weight that may contain minor amounts ofchain branching or co-monomers not exceeding 5 modifying units per 100main chain carbon atoms, and that may also contain admixed therewith notmore than about 50 weight percent of one or more polymeric additivessuch as alkene-1-polymers, in particular low density polyethylene,propylene, and the like, or low molecular weight additives such asanti-oxidants, lubricants, ultra-violet screening agents, colorants andthe like which are commonly incorporated. Such is commonly known asextended chain polyethylene (ECPE). Similarly, polypropylene is apredominantly linear polypropylene material of preferably more than onemillion molecular weight. High molecular weight linear polyolefin fibersare commercially available.

Polybenzoxazole and polybenzothiazole are preferably made up of polymersof the following structures:

While the aromatic group shown joined to the nitrogen atoms may beheterocyclic, they are preferably carbocyclic; and while they may befused or unfused polycyclic systems, they are preferably singlesix-membered rings. While the group shown in the main chain of thebis-azoles is the preferred para-phenylene group, that group may bereplaced by any divalent organic group which does not interfere withpreparation of the polymer, or no group at all. For example, that groupmay be aliphatic up to twelve carbon atoms, tolylene, biphenylen,bis-phenylene either, and the like.

A further requirement in the present invention is the use of a resin tobind individual fibers of the high strength fibers in the employedfabric. The resin may be selected from a wide variety of components suchas polyethylene, ionomers, polypropylene, nylon, polyester, vinyl ester,epoxy and phenolics and thermoplastic elastomers.

The resin may be applied to the fabric containing high strength fibersby coating or impregnation, such as under pressure.

Accordingly, the high strength fabric/resin combination must have anability for deflection within the layered composite when tested inaccordance with National Performance Criteria for Tornado Shelters,First Addition, FEMA, May 28, 1999 using ASTM Test Method E1886-97,entitled “Standard Test Method for Performance of Exterior Window,Certain Walls, Doors and Storm Shutters Impacted by Missile(s) andExposed to Cyclic Pressure Differentials.” Highlights of the testinclude mounting the test specimen, impacting the specimen with a 6.8kilogram (15 pound) 2×4 missile propelled-at a speed of 161 kilometers(100 miles) per hour and observing and measuring the test results. TheASTM test procedure E1886-97 is specific to the various requirementssuch as the use of 2×4 lumber missile, missile propulsion device, speedmeasuring system and use of a high-speed video or photographic camera.It is understood, herein, that the test procedure for purposes of thepresent disclosure, involves attaching any test specimen to a suitablesupport frame, in such a way that is representative of an actual wallinstallation. Such specimen is then impacted on the plywood face at ornear the center of the panel. The 2×4 lumber missile should be markedwith suitable indexing marks to allow the tracking of the depth ofpenetration of the projectile. The photographic or video camera shouldbe positioned to monitor the depth of penetration of the projectile andsuch camera should have a minimum frame rate of 1000 frames per second.

In accordance with the described test procedure, the fabric containinghigh strength fibers bonded with a resin will deflect within a rangefrom 5.0 to 17.5 cm. More preferably, the deflection will be in a rangefrom 8.0 to 16.0 cm and most preferably 10.0 to 15.0 cm. It isunderstood the deflection of the fabric would be typically performed ina separate test procedure on a sheathing (such as plywood)/fabriccombination which is not bonded to one another. In such case thesheathing/fabric separate from one another in the test procedure.

The degree of deflection may be determined by its final use in abuilding structure. Illustratively, a maximum stated deflection of thefabric/resin combination may be undesirable in a residence due to theproximity of an occupant adjacent a wall containing the cloth/resincombination. However, a minimum deflection within the above range canrequire an added thickness of the fabric resulting in a high cost ofconstruction. As employed herein, fabric is inclusive of more than onelayer of a cloth. As employed herein deflection means the maximummeasured distance of separation of the high strength fabric/resincombination from the structural sheathing (i.e. the separation due tothe impact). As previously stated the test procedure is undertaken whenthe high strength fabric/resin combination is not bonded to thesheathing. It is understood that the measurement must be undertaken inconjunction with high-speed photography. For purposes of illustrationfor deflection measurement, if during the test procedure with theprojectile, there may be some bowing of the structural sheathing. Themeasurement for deflection is the distance, i.e., the separation, of thehigh strength fabric/resin combination from the bowed portion of thesheathing. It can be determined from review of the photographic or videorecord collected during previously described testing, determining themaximum depth of penetration during the event, and subtracting thethickness of the structural sheathing.

In the present invention the combination of the fabric containing thehigh strength fibers/resin is for employment with a wood based or otherstructural sheathing material, since an additional purpose of thecombination is the structural reinforcement of a wall or door. The term“structural sheathing” is inclusive of any material which providesstructural building support. The preferred material is wood,particularly plywood, due to extensive use in the building industry.However other materials are known for structural sheathing serving asbuilding support: a typical example is fiberboard reinforced withcement. The fabric/resin combination is generally flexible and will beemployed with the sheathing which for purposes of illustration may be atleast 0.65 cm (one quarter inch) and preferably for purposes of support,at least 1.27 cm (one half inch). The type of structural sheathing isnot critical to the success of the present invention. The sheathing maybe solid such as from hard or soft woods or may be in the form of acomposite such as plywood or a non-wood sheathing such as cementousfiberboard plastic composite and thin gauge metal. As a practicalmatter, it is believed that most uses of the present invention will bewith plywood since it is a common material used in wall structures.There is no maximum thickness to the structural sheathing which in abuilding structure will be or face an outer wall with the combination offabric/resin facing the inner portion of the building, i.e., for examplea room where inhabitants are to be protected.

In accordance with the present invention, structural sheathing will bepresent on opposite faces of the composite holding the remainingcomponents in a sandwich construction. It is understood that the layersof structural sheathing need not be identified.

Therefore, in construction of a protective shelter or one or more roomsin a residence, it is intended that the structural sheathing face thedirection of any wind-borne debris such that the debris strikes thesheathing with penetration before contact and containment withdeflection of the combination of cloth/resin. It is understood that theinvention is particularly advantageous since conventional buildingconstruction and techniques with structural sheathing may be employed.

In the present invention an improvement is present for wind as well asimpact or striking resistance through use of a the following compositeconstruction present in order:

structural sheathing

adhesive

bonded higher strength fiber

adhesive

lightweight material adhesive

adhesive

a structural sheathing

The lightweight material will have a density of not greater than 0.25grams per cubic centimeter, preferably, not greater than 0.10 grams percubic centimeter, and more preferably, not greater than 0.05 grams percubic centimeter.

The lightweight material may be flexible or rigid. However, it is withinthe scope of the present invention for rigidity to be provided bysupport or reinforcement of the lightweight material. Therefore, thelightweight material may not be self-supporting but the overalllightweight material layer will have flexibility or rigid through use ofa support or reinforcement to provide this property. Therefore, in apreferred mode, the layer containing the lightweight material isself-supporting, i.e., it will not collapse. In this preferred mode,sufficient shear modulus and shear strength is needed in the lightweightmaterial to provide for the wind pressure resistance. The needed shearstiffness and strength can be calculated from common design formulausing the previous detailed references, depending on the make-up of thestructural skins, thickness of the lightweight core, and length of thecomposite panel being produced. Illustratively, the lightweightmaterials include, for example, polystyrene and polyurethane, which canbe present as foams or honeycomb structures made, for example, fromkraft paper, aramid paper, aluminum sheeting and plastic. For a nominal4 foot wide by 8-foot long composite panel, having a core thickness of 4inches, the lightweight material will typically need a shear modulusgreater than 300-pounds/square inch and a shear strength greater than25-pounds/square inch to provide resistance to 250 mile per hour winds.These properties are typically present in expanded polystyrene foam witha density greater than 1.0 pound/cubic foot. The lightweight materialcan as well be a foam structure reinforced with light-gauge steelmembers or wires as described in U.S. Pat. No. 4,241,555. However, suchuse is not necessary due to use of an adhesive on opposite sides of thelightweight material.

The thickness of the lightweight material layer is not critical with anexample in the range of 5.0 to 20.0 centimeters. When thinnerlightweight materials are used, the shear strength and shear modulusmust be higher to provide for the wind resistance. When thickerlightweight materials are used, the shear modulus and shear strength canbe lower.

In addition to use of a bonded high strength fabric, three layers ofadhesive are employed, namely (a) between structural sheathing, andmaterial having a density not greater than 0.25 grams per cubiccentimeter), (b) between the material having a density not greater than0.25 grams per cubic centimeter and fabric containing high strengthfibers bonded with a resin and, (c) fabric containing high strengthfibers bonded with a resin and structural sheathing. The types ofadhesive are not considered critical and can be the same resins asdescribed for bonding the high strength fibers, but adhesives mustprovide sufficient bond strength to make the composite act as a singleunit resisting bending under the pressure created by the impinging wind.

To further illustrate the present invention, the following examples areprovided.

EXAMPLE 1

A 48-in by 86-in laminated wall panel was produced in a pneumatic platenpress by stacking in sequence the following materials:

-   -   1. One sheet of plywood, 23/32-inch thick, APA rated sheathing.    -   2. One layer of ISOGRIP® 3030 Urethane Adhesive at 20 gms/sq-ft.    -   3. One layer of 4-inch thick, expanded polystyrene foam core,        with a density of 1.0 lb/cu-ft.    -   4. One layer of ISOGRIP® 3030 Urethane Adhesive at 20 gms/sq-ft.    -   5. Three ply's of Kevlar® Style 745 fabric (13 oz/sq-yd weight)        that had been thermally bonded together with a polyolefin        bonding resin.    -   6. One layer of ISOGRIP® 3030 Urethane Adhesive at 20 gms/sq-ft    -   7. One sheet of plywood, 15/32-inch thick, APA rated sheathing.

The glue was applied as detailed above with an industrial glue rollcoater. The assembled panel was placed in the pneumatic press and heldunder pressure of 7-lbs/sq-in for one hour and the glues allowed tofully cure over 24 hours, before being sent for testing.

The panel was pressure tested in a vacuum rig in accordance with ASTMtest method E72. The panel failed at a pressure of 425 lbs/sq-ft andshowed excessive deformation and a non-linear load deflection cure. Theload deflection curve is shown in the Figure. The ultimate failure loadof this panel would not provide the margin of safety needed for use inthe highly loaded sections of wind shelters, and would not provide theneeded rigidity in the walls to meet typical building standards for loadbearing walls.

An additional 48-in-by-48-in test panel was produced as described aboveto access the ability of the wall to resist the penetration by windbornedebris. The panel was impact tested, with a 15-pound lumber projectileat a speed of 161 kilometers (100 miles) per hour in accordance withASTM test procedure E1886-87. The projectile did not penetrate the wall.

EXAMPLE 2

A 48-in by 86-in laminated wall panel was produced in a pneumatic platenpress as described in Example 1 with 4-inch thick expanded polystyrenefoam core with the density increased to 2.5 lb/cu-ft.

The panel was pressure tested in a vacuum rig in accordance with ASTMtest method E72. The panel failed at a pressure of 673 lbs/sq-ft andshowed low deformation and a linear load deflection cure. The loaddeflection curve is shown in the Figure. The ultimate failure load ofthis panel would provide the margin of safety needed for use in thehighly loaded sections of wind shelters, and would provide the neededrigidity in the walls to meet typical building standards for loadbearing walls.

An additional 48-in-by-48-in test panel was produced as described aboveto access the ability of the wall to resist the penetration by windbornedebris. The panel was impact tested, with a 15-pound lumber projectileat a speed of 161 kilometers (100 miles) per hour in accordance withASTM test procedure E1886-87. The projectile did not penetrate the wall.

An additional 48-in by 86-in laminated wall panel was produced in apneumatic plated press as described above. This panel was impact testedin a shelter room assembly connected together with flexible joints asdetailed in US patent application KB 4640 US NA. Impact testing was donewith a 15-pound lumber projectile at a speed of 161 kilometers (100miles) per hour in accordance with ASTM test procedure E1886-87. Theprojectile did not penetrate the wall panel.

EXAMPLE 3

A 48-in by 86-in laminated wall panel was produced in a pneumatic platenpress as described in Example 1 with 4-inch thick expanded polystyrenefoam core with the density increased to 3.0 lb/cu-ft.

The panel was pressure tested in a vacuum rig in accordance with ASTMtest method E72. The panel failed at a pressure of 673 lbs/sq-ft andshowed low deformation and a linear load deflection cure. The loaddeflection curve is shown in the Figure. The ultimate failure load ofthis panel would provide the margin of safety needed for use in thehighly loaded sections of wind shelters, and would provide the neededrigidity in the walls to meet typical building standards for loadbearing walls.

An additional 48-in-by-48-in test panel was produced as described aboveto access the ability of the wall to resist the penetration by windbornedebris. The panel was impact tested, with a 15-pound lumber projectileat a speed of 161 kilometers (100 miles) per hour in accordance withASTM test procedure E1886-87. The projectile did not penetrate the wall.

1. A composite comprising in order: (a) a layer of structural sheathing,(b) a layer of adhesive, (c) a layer of material having a density notgreater than 0.25 grams per cubic centimeter, (d) a layer of adhesive,(e) a layer of a fabric containing high strength fibers bonded with aresin, (f) a layer of adhesive, (g) a layer of structural sheathing.wherein the fabric layer will deflect in a range from 5.0 to 17.5centimeters when impacted by a 6.8-kilogram (15 pound) projectile at aspeed of 161 kilometers (100 miles) per hour in accordance with ASTMtest procedure E1886-97.
 2. The composite of claim 1 wherein thedeflection is in a range from 8.0 to 16.0 centimeters.
 3. The compositeof claim 1 wherein the high strength fibers are selected from the groupconsisting of aramid fibers, glass fibers, polyethylene fibers,polyvinyl alcohol fibers, polyarylate fibers, polybenzazole fibers, orcarbon fibers.
 4. The composite of claim 1 wherein the high strengthfibers comprise an aramid.
 5. The composite of claim 1 wherein the highstrength fibers are glass.
 6. The composite of claim 1 wherein thestructural sheathing comprises plywood.
 7. The composite of claim 1wherein layer (c) has a density not greater than 0.10 grams per cubiccentimeter.
 8. The composite of claim 1 wherein layer (c) is a foam. 9.The composite of claim 1 wherein layer (c) has a honeycomb orhoneycomb-like structure.
 10. A building structure having an integralportion of the structure comprising: (a) a layer of structuralsheathing, (b) a layer of adhesive, (c) a layer of material having adensity not greater than 0.25 grams per cubic centimeter, (d) a layer ofadhesive, (e) a layer of a fabric containing high strength fibers bondedwith a resin, (f) a layer of adhesive. wherein the fabric layer willdeflect in a range from 5.0 to 17.5 centimeters when impacted by a6.8-kilogram (15 pound) projectile at a speed of 161 kilometers (100miles) per hour in accordance with ASTM test procedure E1886-97.